The Role of Nucleus and Cytoplasm 



145 



derm and entoderm of a normal egg of the 

 maternal species. The resulting plutei always 

 showed the skeletal characteristics of the 

 species which furnished the nucleus of the 

 micromeres. 



The numerous experiments on hybrid an- 

 drogenesis in amphibians show that develop- 

 ment proceeds to more advanced stages in 



of T. palmatus or T. alpestris showed that 

 various tissues with T. taeniatus or T. pal- 

 matus cytoplasm and T. cristatus nucleus 

 may survive and differentiate normally. Of 

 particular interest is Hadorn's experiment 

 ('36) illustrated in Figure 37, in which a 

 large graft of androgenetic hybrid skin on an 

 alpestris host survived beyond metamorpho- 





9 gos. 



^S^^^R^^<^^^4 



c=,o g> "lo ^ i^ ybi 



Fig. 37. Demonstration of effect of egg cytoplasm on development of skin characteristics appearing after 

 metamorphosis (after Hadom, '36). a, Fertilization of egg of Triturus palmatus with sperm of T. cristatus 

 followed by removal of egg chromosomes, b and c, A large piece of presumptive epidermis from androgenetic 

 hybrid gastrula, stained with nile-blue sulfate, is transplanted to diploid gastrula of a third species, T. 

 alpestris. d. Transplant survives and covers large part of left flank of host embryo, e, Same animal after 

 metamorphosis; skin removed from transplant has taken part normally in transformation. /, Diagrammatic 

 section through epidermis of metamorphosed T. palmatus showing typical projections formed by series of 

 flattened epidermis cells, g, Section through epidermis of metamorphosed T. cristatus with smooth surface. 

 h, Section through epidermis formed by transplant (cells contain T. palmatus cytoplasm and haploid T. 

 cristatus nuclei) ; typical protuberances are present as in T. palmatus epidermis. 



combinations between more closely related 

 species than in "distant" combinations; how- 

 ever, none of the androgenetic hybrids reach 

 a stage in which differential characteristics 

 of the two species appear (Table 8). A de- 

 tailed analysis of the combination T. taenia- 

 tus (or T. palmatus) cytoplasm with T. cris- 

 tatus nucleus by Baltzer ('30b, '33, '40) and 

 Hadom ('30 to '37) revealed that the early 

 death is caused by the disintegration of the 

 head mesenchyme. Cultivation of other re- 

 gions of the young gastrula in vitro and, par- 

 ticularly, transplantation to normal embryos 



sis and developed the epidermal protuber- 

 ances that are typical for T. taeniatus which 

 contributed the cytoplasm, but absent in 

 T. cristatus, the donor of the nucleus. This 

 result is probably to be explained as a ma- 

 ternal effect, due to the early activity of the 

 T. taeniatus genome in the growing oocyte, 

 before fertilization, although the character- 

 istic does not appear until several months 

 later (cf. Baltzer, '40). Normal histological 

 differentiation of various organs has also 

 been obtained in transplants from gastrulae 

 of the combination T. alpestris cytoplasm 



